Regular maintenance is carried out on an inkjet head of an inkjet recording device, including removal of highly viscous ink that has adhered to a nozzle of the inkjet head. Highly viscous ink is produced when the solvent in the ink that has adhered to the nozzle evaporates. Such highly viscous ink is removed by circulating ink through the nozzle while applying negative pressure thereon. The highly viscous ink may also be removed by purging the ink being ejected from the inkjet head.